1. Field of the Invention:
THIS INVENTION RELATES TO YARN FEEDING AND, MORE PARTICULARLY TO THE CONTROLLED DELIVERY OF YARN FROM A YARN SOURCE TO A FEEDING MEANS SUCH AS A NEEDLE.
2. Description of the Prior Art:
There is a wide variety of products which are formed by feeding one or more lengths of yarn through a backing material. Usually, each length of yarn is fed through the backing material by successive movements of a needle or similar device and in many of these products it is desired that each length of yarn fed through the backing material be varied in a predetermined manner with successive movements of the needle or similar device. Typical of products of this type are tufted fabrics in which loops of yarn define a pattern.
It is to the production of products such as tufted fabrics that the invention disclosed herein is ideally suited. This is because such products characteristically require that the lengths of yarn fed through a backing material be delivered to a needle or similar device in a controlled manner in order to provide loops of yarn of a selected height or of a plurality of selected heights and because such yarn length control has not been satisfactorily provided by the prior art.
For example, loop length control in the prior art has generally been achieved by controlling the length of yarn delivered to a needle throughout each stitching cycle of a tufting machine. Since the length of yarn which must be delivered throughout a stitching cycle for a loop of yarn of relatively low height is less than the length of yarn which must be delivered throughout s stitching cycle for a loop of yarn of greater height, the yarn is usually delivered at different yarn delivery rates to a needle during successive stitching cycles.
In the prior art, this change in yarn delivery rate from one stitching cycle to the next is generally not well defined and causes a pattern formed by loops of yarn of varying height to be poorly defined. Moreover, this change in yarn delivery rate from one stitching cycle to the next places the yarn during successive stitching cycles under varying degrees of tension. With yarn having a relatively high degree of elasticity, these varying degrees of tension, in the relatively long lengths of yarn which characterize yarn length control in the prior art, result in slackening and tightening of the lengths of yarn and in conditions such as bowstring vibrations in the lengths of yarn, friction between adjacent lengths of yarn, frequent entanglement of adjacent lengths of yarn, and where fluid pressure is being used to feed the lengths of yarn, variations in the amount of fluid pressure required to feed the yarn. When any of these conditions exists in the delivery of yarn, it is difficult to avoid frequent yarn breakage or to prevent one loop of yarn from having different characteristics from another loop of yarn.
It is also characteristic of yarn length control in the prior art for the length of yarn delivered to a needle for forming a loop of yarn of a particular height to include not only that length of yarn required for the loop of yarn but also that length of yarn required for a back stitch. Thus, the change in yarn delivery rate from one stitching cycle to the next which is generally characteristic of yarn length control in the prior art also results in those particular lengths of yarn required for the formation of back stitches being delivered over varying portions of the stitching cycles, each portion being dependent upon yarn delivery rate. The formation of back stitches can be more uniform if the particular length of yarn required for a back stitch is delivered to a needle during that portion of each stitching cycle in which back stitches are formed. Such uniformity is difficult to achieve where backstitch lengths of yarn, as in the prior art, are delivered during the loop forming portions of the stitching cycles.
Moreover, the failure of yarn length control in the prior art to deliver a particular length of yarn, such as the length of yarn required for a back stitch, during a particular portion of a stitching cycle, rather than during the entire stitching cycle, makes that coordination between needle motion and the delivery of a length of yarn which is necessary for the formation of floats on the back of a tufted fabric difficult to achieve. Either a failure to achieve this coordination or the lack of back stitch uniformity frequently encountered in the prior art will serve to cause a lack of uniformity in loops of yarn and poor pattern definition.
Yarn length control in the prior art is not only characterized by the foregoing and other difficulties in controlling the length of yarn delivered to a needle, but it is also frequently characterized by limitations in the variations in the lengths of yarn which can be obtained and in the speed at which they can be obtained. These limitations in turn limit the variety of patterns which can be obtained for a tufted fabric and the speed at which a tufting machine may be operated.
Where these limitations have been individually avoided in the prior art, they have been avoided only by the use of apparatus in which the means for delivering the varying lengths of yarn required for a pattern is difficult and expensive to manufacture and maintain. Moreover, almost all apparatus required for yarn length control in the prior art have caused expensive down time of a tufting machine when a change in pattern is desired.